Communication of information signals on a point-to-point basis in an optical fiber network is most practically achieved by impressing information signals on optical carriers and routing these optical information signals to the desired destination on the basis of optical wavelength, a technique known as wavelength division multiplexing. In a wavelength division multiplexed optical network, optical information signals are transmitted via optical fibers between a central office and a plurality of optical network units at a plurality of discrete optical wavelengths. Each optical network unit receives and transmits an optical information signal at a specific, predetermined optical wavelength. A remote node interposed between the central office and the plurality of optical network units routes the optical information signals between each of the optical network units and the central office according to optical wavelength.
Presently, wavelength division multiplexed optical networks, such as the RITE-Net, described in N. J. Frigo et al., "RITE-Net: A Passive Optical Network Architecture Based on the Remote Interrogation of Terminal Equipment," OFC '94 Postdeadline papers, pp. PD8-1 to PD8-3 (1994), and incorporated by reference herein, utilize a plurality of discretely tunable optical sources, such as lasers, to send information signals, known as downstream information or downstream traffic, from the central office to the optical network units. Optical information signals at a plurality of discrete wavelengths are obtained by tuning the laser, in succession, to a discrete wavelength and then modulating the optical power emitted by the laser using techniques well known in the art. For the transmission of optical information signals from the plurality of optical network units to the central office, known as upstream information or upstream traffic, a modulator in each optical network unit imprints an information signal on a continuous wave portion of the downstream signal that was routed to the optical network unit over a first optical fiber. Each upstream signal is coupled from the optical network unit into a second optical fiber for routing through the remote node to the central office.
There exists, however, a need for a more economical and efficient wavelength division multiplexing network architecture. A tunable laser may emit only one optical wavelength at a time, a well known characteristic of time division multiplexing (TDM), and, therefore, inefficiently utilizes the time dimension of a transmission path. In addition, the optical receiver of an optical network unit must operate at the full aggregate bit-rate. Further, two optical fibers are required for connecting each optical network unit to the remote node. Finally, the use of modulators in optical network units is not-yet economical.